Resource Utilization by the ATLAS High Level Trigger during 2010 and 2011 LHC running

Abstract

Since starting in 2010, the Large Hadron Collider (LHC) has produced collisions at an ever increasing rate. The ATLAS experiment successfully recorded the collision data with high efficiency and excellent data quality. Events were selected using a three-level trigger system, where each level made a more refined selection. The Level 1 (L1) trigger consisted of a custom-designed hardware trigger which seeded two higher software based trigger levels. Over 300 triggers composed a trigger menu which selected physics signatures such as electrons, muons, particle jets, etc. Each trigger consumed computing resources of the ATLAS Trigger system and offline storage. The LHC instantaneous luminosity conditions, desired physics goals of the collaboration, and the limits of the trigger infrastructure determined the composition of the ATLAS Trigger menu. We describe a trigger monitoring framework called the Cost Monitoring Framework for computing the costs of individual trigger algorithms such as data request rates and CPU consumption. This framework was used to prepare the ATLAS Trigger for data taking during increases of more than six orders of magnitude in the LHC luminosity and has been influential in guiding ATLAS Trigger computing upgrades.